uint fee = getTransferFee(keyOwner, _timeShared);
uint timePlusFee = _timeShared + fee;
if(timePlusFee < timeRemaining) {
  // now we can safely set the time
  time = _timeShared;
  // deduct time from parent key, including transfer fee
  _timeMachine(_tokenId, timePlusFee, false);
} else {
  // we have to recalculate the fee here
  fee = getTransferFee(keyOwner, timeRemaining);
  // @audit want it such that time + fee * time == timeRemaining, but fee is taken on timeRemaining instead of time
  time = timeRemaining - fee;
}
